Linear drive for integrated damper

ABSTRACT

A housing assembly having an integrated damper with a linear drive mechanism is provided. In one embodiment, the housing assembly includes a housing having an inlet and an outlet. A damper is disposed in the housing and is positionable to regulate flow entering the housing through the inlet. A linear drive mechanism is operably coupled to the damper and is adapted to linearly move the damper between positions that are spaced-apart from the housing and a position that closes the inlet. The linear drive mechanism is configured to move the damper linearly without rotating the damper.

This application claims benefit from U.S. Provisional Patent ApplicationSer. No. 60/729,644, filed Oct. 24, 2005, which is incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a housing assembly having anintegrated damper, and more specifically, a housing assembly for an airfilter having an integrated damper with a linear drive mechanism.

2. Description of the Related Art

Cleanrooms are utilized in many industries for contamination control andto improve product yields. A plurality of filters, typically mounted inthe ceiling of the cleanroom, are configured to remove particulate fromair entering the cleanroom at a predetermined efficiency selected basedupon the cleanliness requirements of the activities performed in thecleanroom. As particulates load the filtration media disposed in thefilter, the airflow through the filter decreases as the pressure dropacross the filter increases. Once the filter reaches a critical pressuredrop, the filter is typically replaced.

On other applications, replacement of filters is scheduled based on timeor processes performed within the cleanroom. For example, in manypharmaceutical and biotech cleanrooms, periodic replacement of filtersis required to meet regulatory or owner specifications. To facilitateefficient replacement of the filter, a hood (housing) is typicallymounted in the cleanroom ceiling in which the filter may be readilyremoved and replaced.

Ducted supply hoods with roomside replaceable filters are commonly usedin pharmaceutical applications for cleaning supply air to cleanroommanufacturing and process areas, as well as to laboratory areas. Most ofthese hoods are supplied with adjustable dampers that allow customers toregulate the airflow without having to remove the filter from the hood.The most common types of dampers are guillotine, opposed blade andbutterfly types. When completely closed, these dampers essentially stopthe flow of air to the hood. In many cases, the leakage through a closeddamper is negligible in terms of flow rate, but is significant whenconsidered in the terms of contamination of a cleanroom.

Because these types of dampers do not provide a seal (i.e., are notleak-free or bubble-tight), they are inadequate when it comes todecontamination processes that require complete isolation of thecleanroom. For example, during routine testing and validation of filtersinstalled in a pharmaceutical facility, one or more filters may be founddamaged, leaking and/or requiring replacement. When a technician removesthat filter from the hood, the “seal” between the cleanroom and thecontaminated plenum and supply ducts upstream of the removed filter isbroken. When the new filter is installed, the “seal” between those twoareas is restored, but the cleanroom has already been contaminated byair and particulate entering the cleanroom from the contaminated area ofthe plenum and supply ducts. Thus, the facility owner must perform adecontamination process of the entire room before resuming cleanroomoperations. This is a very time-consuming and costly process.

Therefore, there is a need for a filter housing assembly having improvedsealing capabilities.

SUMMARY OF THE INVENTION

Embodiments of the invention generally include a housing assembly havingan integrated damper with a linear drive mechanism. In one embodiment, ahousing assembly includes a housing having an inlet and an outlet. Adamper is disposed in the housing and is positionable to regulate flowentering the housing through the inlet. A linear drive mechanism isoperably coupled to the damper and is adapted to linearly move thedamper between positions that are spaced-apart from the housing and aposition that closes the inlet. The linear drive mechanism is configuredto move the damper linearly without rotating the damper.

In another embodiment, a housing assembly includes a housing having aninlet and outlet. A damper is disposed in the housing and is linearlymovable between positions that open and close the inlet. The damper hasa non-planar shape that extends into the inlet when the damper is in aclosed position. A means is provided for restraining the damper fromrotating.

In another embodiment, a housing assembly includes an inlet port, anoutlet port and a bag in/bag out filter access port. A filter receivingmechanism is disposed in the housing and is configured to direct gasesflowing between the inlet and outlet ports through a filter installed inthe housing. A first damper is disposed in the housing and is movablebetween positions that open and close the inlet port. A second damper isalso disposed in the housing and is movable between positions that openand close the outlet port. A mechanism is provided in the housing thatis configured to move the first damper between the open and closedpositions without rotating the first damper, wherein the first damper isspaced apart from the housing when in the open position.

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the present invention can be readily understood byconsidering the following detailed description in conjunction with theaccompanying drawings, in which:

FIG. 1 is a cross-sectional view of one embodiment of a linear damperassembly disposed in a filter housing assembly;

FIG. 2 is a partial sectional view of the housing assembly of FIG. 1;

FIG. 3 is a top view of a portion of an actuator adapted for linearlymoving a dish of the damper assembly;

FIG. 4 is a side view of a bushing;

FIG. 5 is a partial side view of a rack of the actuator;

FIG. 6 is a side cut-away view of one embodiment of a linear damperassembly disposed in a contamination housing assembly;

FIG. 7 is another embodiment of a linear damper assembly disposed in ahousing assembly;

FIG. 8 is a perspective view of one embodiment of the linear damperassembly in an open position; and

FIG. 9 is a perspective view of the linear damper assembly in a closedposition.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

It is to be noted, however, that the appended drawings illustrate onlyexemplary embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

DETAILED DESCRIPTION

Selected Embodiments of the Apparatus

FIG. 1 is a sectional view of one embodiment of a filter housingassembly 100 having a linear damper assembly 130. Although the housingassembly 100 is depicted in FIG. 1 as a room-side replaceable filtermodule, it is contemplated that the benefits and features of theinvention may be incorporated in contamination housings, filterdiffusers, damper modules and other devices where robust flow control isdesired in applications for cleanrooms, environmental and contaminantcontrol, air conditioning, heating and ventilation systems, among otherapplications.

The housing assembly 100 generally includes a housing 102 having aninlet 104 and an outlet 106. The inlet 104 and the outlet 106 are formedthrough the housing 102 and allow gases flowing through a duct 110,shown in phantom, to be routed through the housing 102. The inlet 104 isbounded by a collar 112 to facilitate coupling the duct 110 to thehousing 102. A filter element 108 is disposed in the outlet 106 and issealingly coupled to the housing 102 in a manner that causes gasesflowing between the inlet 104 and the outlet 106 to pass through thefilter element 108. The filter element 108 may be retained in thehousing 102 in any suitable manner, for example by a clip 120 orfastener.

In the embodiment depicted in FIG. 1, the housing 102 includes aninternal flange 114 that sealingly engages the filter element 108. Inone embodiment, the flange 114 includes a knife-edge 116 that sealinglyengages a seal 118 coupled to the filter element 108. The seal 118 mayalternatively be coupled to the housing 102. The seal 118 may be a fluidseal, such as a gel, a gas gasket or other material suitable forproviding a seal between the housing 102 and filter element 108. It isalso contemplated, as in diffuser applications, that the filter element108 may be potted, bonded, adhered or permanently coupled to the housing102.

The damper assembly 130 is disposed in the housing 102 between the inlet104 and the filter element 108. The damper assembly 130 generallyincludes a damper dish 132, a linear drive mechanism 136 and a bracket144. The bracket 144 is coupled to the housing 102. The bracket 144generally supports and positions the dish 132 and linear drive mechanism136 within the housing 102. The linear drive mechanism 136 is configuredto move the dish 132 linearly to open and close the inlet 104.

Referring back to FIG. 1, the linear drive mechanism 136 may be anyactuator suitable for causing the dish 132 to move linearly withoutrotation. For example, linear drive mechanism 136 may be a power screw,solenoid, electric motor, pneumatic cylinder, hydraulic cylinder or cam,scissor actuator, linear actuator among others. In the embodimentdepicted in FIG. 1, the actuator 138 includes a rack 138 and a gear 140.The rack 138 is coupled to a dish 132 by a fastener 134. It iscontemplated that the dish 132 may be coupled to the rack 138 by othersuitable fastening methods. To insure a perpendicular orientationbetween the dish 132 and the rack 138, the dish 132 includes a flatcenter section 162 that seats against the flat end of the rack 138.

In the embodiment depicted in FIG. 1, the gear 140 is a pinion gear,although another gear or gears may be utilized. The pinion gear 140 iscoupled to a shaft 152. The size of the pinion gear 140 may be selectedto provide a predetermined stroke of the rack 138, and to provide apredetermined actuation force. In one embodiment, the shaft 152 extendsthrough the housing 102 such that the rotational orientation of thepinion gear 140, and thus, the position of the rack 138 and dish 132,may be controlled. The shaft 152 may include a key or other suitableconnection with the pinion gear 140 that insures efficient transfer ofmotion between the shaft 152 and pinion gear 140. In one embodiment, theintermeshing teeth of the rack 138 and pinion gear 140 include flatcrests and trenches that prevent the dish 132 from rotating as the rack138 is advanced. The flat crests and trenches of the rack 138 areillustrated in FIG. 5, with the pinion gear 140 being similarlyconfigured. It is contemplated that the linear drive mechanism may haveother configurations that prevent rotation of the dish 132, including,but not limited to, keyed retaining features, tracks, multiple bearingguides, and the like.

The rack 138 is slidably mounted through a set of bushings 142 that arecoupled to the bracket 144. The bushings 142 may be comprised of anysuitable bearing material, such as DELRIN® or brass. The bushings 142may alternatively be roller bearings. The rack 138 may be exchanged toprovide longer or short actuation strokes which correspondingly sets theorifice area between the dish 132 and the inlet 104.

In the embodiment depicted in FIG. 1, the bracket 144 includes a racksupport 146 having two tabs 148 extending therefrom. The bushings 142are mounted in the tabs 148 in a spaced-apart relation to enhancecontrol of the motion and orientation of the dish 132. The rack support146 is coupled to one or more cross bars 150 extending between oppositewalls of the housing 102. The cross bars 150 may be welded, riveted orfastened to the housing 102.

The dish 132 generally includes a conical face 160 having a sealingsection 164 located adjacent a perimeter 166 of the dish 132. Thesealing section 164 is adapted to engage the housing 102 and/or thecollar 112 in a manner that facilitates sealing the air flow through theinlet 104. In the embodiment depicted in FIG. 1, the sealing section 164includes a channel 168 having a seal 170 disposed therein. The seal 170is configured to engage with a lip 172 extending from one of the collar112 or the housing 102. The seal 170 may be a gasket, bladder or fluidseal. It is also contemplated that the seal 170 may be coupled to thecollar 112 or the housing 102 and configured to sealingly engage withthe dish 132. The non-rotation of the dish 132 provided by the rack 138and pinion gear 140 discussed above, prevents shearing of the seal asthe dish 132 and lip 170 engage, thereby extending the life andperformance of the seal. It is contemplated that the dish 132 may rotatewhen spaced from the closed position, as long as the linear drivemechanism 136 does not cause the dish 132 to rotate while sealing theinlet 104.

FIG. 2 depicts a partial sectional view of the housing 102 illustratingthe shaft 152 extending through the housing 102. To prevent leakage fromthe housing assembly 100 around the shaft 152, a bushing 202 is sealablyfastened around a hole 204 formed through the housing 102 to facilitatepassage of the shaft 152. The bushing 202 may be sealed to the housing102 by any suitable method. In the embodiment depicted in FIG. 2, thebushing 202 is continuously welded to the housing 102.

A bearing 206 is press-fit into the bushing 202 and engages the shaft152 to facilitate rotation. A seal 208 is disposed in one end of thebushing 202 to prevent air leakage between the bushing 202 and the shaft152. The seal 208 may be an o-ring, cup seal, gasket, fluid seal orother seal suitable for preventing leakage of gas around the shaft 152and through the hole 204 of the housing 102.

The shaft 152 includes terminal end 250 disposed outside the housingassembly 100. The terminal end 250 generally includes a drive feature252 that facilitates inducing rotational motion to the shaft 152. In oneembodiment, the drive feature 252 is a flat formed in the sides of theshaft 152. Other suitable drive features include, but are not limitedto, hex heads, knurled surface, key ways, slots and the like. Althoughthe terminal end 250 is shown extending from the side of the housing102, it is contemplated that the drive feature 252 may be accessiblefrom the other locations, such as from the outlet-side of the housing100.

Referring to FIGS. 3-4, the inner end of the shaft 152 proximate thepinion gear 140 is supported by a second bearing 304. The second bearing304 is disposed in a tab 302 extending from the rack support 146. Thesecond bearing 304 may be similar to the bearing 206.

In operation, the shaft 152 is selectively rotated to rotate the piniongear 140. The rotating pinion gear 140 advances the rack 138, therebylinearly moving the dish 132. As the motion of the dish 132 issubstantially perpendicular to the plane of the opening defined by theinlet 104, the seal 170 uniformly engages the lip 172, thereby enhancingseal uniformity and performance. Moreover, as the dish 132 is maintainedcentered relative to the flow entering (or exiting) the housing 102through the inlet 104, the flow orifice defined between the dish 132 andlip 172 is uniform, thus, promoting flow uniformity through the filterelement 108. The dish 132 is illustratively shown in a position closingand spaced from the inlet 104 in FIGS. 8-9. The spacing of the dish 132from the lip 172 may be selected to provide a desired air flow ratethrough the filter element 108.

FIG. 6 is a sectional view of one embodiment of a contamination housingassembly 600. A contamination housing assembly that may be adapted tobenefit from the invention is available from Camfil Farr, Inc., locatedin Riverdale, N.J.

In one embodiment, the housing assembly 600 includes a housing 602having an inlet 604, an outlet 606 and at least one access port 608. Theinlet 604 and outlet 606 are formed through the housing 602 and arrangeto direct gases flowing through the housing 602. The access port 608 isconfigured to permit access to the interior of the housing 602, forexample, for filter change-out, scanning a filter disposed in anadjacently coupled housing, and the like.

The housing 602 may be fabricated from a metal, such as aluminum, steeland stainless steel, or other suitable material. The housing 602 has aconstruction that forms a pressure barrier between gases flowingtherethrough and an environment outside the housing 602. In theembodiment depicted in FIG. 6, the housing 602 is a hollow rectangularbody fabricated from continuously welded metal sheets.

The housing 602 additionally includes sealing flange 614 that sealinglyengages a filter element 616 disposed in the housing assembly 600. Alinkage mechanism 620 is provided in the housing 602 and is configuredto move the filter element 616 between a position sealingly engaged withthe flange 614 and a position clear of the flange 614. A seal, notshown, like the seal 170 described above, is disposed between the filterelement 616 and flange 164 to prevent flow from bypassing the filterelement 616.

The access port 608 is configured to facilitate removal of the filterelement 616 from the housing 602 and is selectively sealed by a door622. The access port 608 is circumscribed by a bagging ring (not shown)that is utilized to access the interior of the housing and/or remove andreplace the filter element 616.

At least one end of the contamination housing 600 includes a lineardamper assembly 130. The linear damper assembly 130 is as describedabove. In the embodiment depicted in FIG. 6, an external actuator 690 iscoupled to the shaft 152 of the damper assembly 130 on the exterior ofthe housing 602. The external actuator 690 may be any device or objectsuitable for controlling the rotation of the shaft 152. In oneembodiment, the external actuator 690 is a wheel. It is contemplatedthat the external actuator 690 may alternatively be a motor, pneumaticcylinder, hydraulic cylinder or a lever, among others.

FIG. 7 depicts one embodiment of a housing assembly 700 having a damperassembly 130. The housing 700 may be configured with or without anaccess port 608. The housing assembly 700 may be utilized as astand-alone damper (shutoff and/or flow control), or as an access portin a containment system, among others. The damper assembly 130 may beoperated as described with reference to the embodiments above to controlflow through the housing assembly 700.

Life Cycle Testing

A housing assembly having an integrated linear damper assembly asdescribed above was tested to determine if any significant or adverseamount of wear will occur between the fabricated pinion gear and rack(both fabricated from stainless steel); and if any significant oradverse amount of wear will occur in the bronze bushings used to supportthe rack and the damper shaft.

Test Setup

A one-high by one-wide containment housing was modified to accept theintegrated linear damper assembly. The integrated damper assemblyutilized a 12″ diameter stainless steel dish. A medium durometersilicone sponge gasket was cut by hand using a template. RTV was placedin the bottom of the channel of the dish. The gasket was seated in thechannel, using the RTV as an adhesive to hold the gasket in the channel.The edges of the sponge gasket were not sealed in the channel, in orderto test the seal with minimum adhesion to the dish.

The damper actuator included a three quarter inch diameter stainlesssteel shaft with keyway, which is typically used on conventional flatblade dampers. A pinion gear was fabricated from one quarter inch thick304 stainless steel. Three gear pieces were stacked on top of each otherwith the keyways aligned and welded together to form a single gear aboutthree quarter inch thick. The rack was manufactured from 20 mm diameter,304 stainless steel shaft. The rack travels in a linear fashion and washeld in place and aligned using bronze bushings coupled to the bracket.A bronze bushing was also installed in a support member to hold andalign the damper shaft and assure proper meshing of the gear teeth withthe rack.

A lip extending from a 12 inch (304.8 mm) diameter, 304 stainless steelcollar circumscribing the inlet was used to form that knife-edgecircumscribing the inlet. The collar was continuously welded to a pieceof 11 gauge 304 stainless steel that was continuously welded to theupstream flange of the housing.

As an actuator coupled to the damper assembly rotated to turn the piniongear, the rack is advanced linearly toward the inlet. The rack pushesthe stainless steel dish toward the knife-edge mounted in the endplateof the housing. The silicone gasket around the perimeter of the dishsealed against the knife-edge. In one embodiment, the flat form of theteeth of the rack, engaged with the flat form of the teeth of the shaftsubstantially prevents rotation of the shaft.

Test Equipment & Instrumentation

-   Elomatic 350 Series Pneumatic Actuator with spring return    -   Model: ESO350.U2A03B.27K0    -   Serial No.: 22221100020-   Blank-off Plate with Ball Valve and static pressure connection-   OMRON Timer:    -   Model: H3CR-F8300-   Dwyer Flex-Tube Manometer:-   Gast Vacuum Pump    Test Procedure

The damper was bubble-tested in accordance with CFW-1000 CFW-10003,Revision 3: Pressure Decay/Structural Capability/Bubble Leak Testing.The containment housing with integrated damper was placed on a cart anda blank-off plate with ball valve and static pressure port was attachedto the opposite end of the inlet collar that also serves as theknife-edge. This space was pressurized such that the damper was beingpushed away from the knife-edge. The pressure was measured with a U-tubemanometer that provided a differential pressure reading between thepressurized space and atmospheric pressure. Soap solution was sprayed onthe interface between the knife-edge on the inlet ring and the siliconegasket that it was sealing against. Visual inspections were conductedfor a period of 5 minutes to ensure bubble-tightness (i.e., a leak freecondition).

Generally, bubble-tight dampers are bubble-leak tested at >+10″ watergauge (w.g.) (2.50 kPa). In some circumstances, they are required to bebubble-tight at >+15″ w.g. (3.74 kPa). During this test, the lineardamper was tested at >+18″ w.g. (4.48 kPa).

After the initial bubble-test, power and compressed air were supplied tothe actuator, and the damper was cycled between open and closedpositions. Bubble-tests were conducted after more than 5,000, 10,000 and15,000 cycles using the method described above. Visual observations wereconducted throughout the entire test to determine the effect of rapidrepeated cycling on the durability of the seal and actuation mechanism.

Results

The results of the cycle tests are as follows: TABLE 1 Cycle TestResults Cumulative # of Cycles Pressure Pass or Fail Comments 0  >17″w.g. Pass Initial Test (4.23 kPa) 5585  >28″ w.g. Pass Damper was leftclosed the (6.97 kPa) previous night. Indentation in silicone gasket,but still passed the bubble-tight test. No indication of mechanism wear.10,289 >+18″ w.g. Pass Damper was left closed the (4.48 kPa) previousnight. Indentation in silicone gasket, but still passed the bubble-tighttest. No indication of mechanism wear. 15,260 >+18″ w.g. Pass Damper wasleft closed the (4.48 kPa) previous night. Indentation in siliconegasket, but still passed the bubble-tight test. No indication ofmechanism wear.

As shown in Table 1, the damper was bubble-tight at >+18″ w.g. (4.48kPa) for each test conducted. It is believed that the damper wouldremain bubble-tight at higher pressures. The test was terminated after15,260 cycles without failure to facilitate use of the lab for otherprojects. Upon visual observation and inspection of the mechanism fordamper actuation after conclusion of the test, no evidence of mechanismwear, degradation or failure was apparent. There also was no visualevidence of gear wear.

The tested damper assembly compares favorably to conventional flat-bladedampers and dish-style dampers. The extended life is believedattributable to the design and construction of the damper assembly,which utilizes linear motion that has reduce bushing wear and stresscompared to rotating blade. Moreover, the linear motion and the use ofgearing reduces the power required to close the damper, therebyminimizing actuator costs.

CONCLUSIONS

The damper was proven to remain bubble-tight at >+18″ w.g. (4.48 kPa) atmore than 15,000 cycles, which is 50 percent greater than the industryrequirements (bubble-tight at +10″ w.g. (2.50 kPa) after 10,000 cycles).The robustness and durability of the mechanism are superior to both theflat-blade damper and dish-style damper designs, as proven by the lackof wear even after more than 15,000 cycles.

Although various embodiments which incorporate the teachings of thepresent invention have been shown and described in detail herein, thoseskilled in the art can readily devise many other varied embodiment thatstill incorporate these teachings.

1. A housing assembly, comprising: a housing having an inlet and anoutlet; a damper disposed in the housing in an orientation that remainscentered with respect to the inlet; and a linear drive mechanism adaptedto move the damper linearly between positions that open and close theinlet without rotating the damper.
 2. The housing assembly of claim 1,wherein the damper is substantially conical.
 3. The housing assembly ofclaim 1 further comprising: a filter element disposed in the housing. 4.The housing assembly of claim 1, wherein the housing is at least one ofa filter housing, a contamination housing or a stand-alone damper. 5.The housing assembly of claim 1, wherein the linear drive mechanism isat least one of a cam, a scissor actuator, a linear actuator, a powerscrew, a solenoid, an electric motor, a pneumatic cylinder, a hydrauliccylinder or a gear.
 6. The housing assembly of claim 1 furthercomprising: a seal interfacing the damper and the housing to providing abubble-tight seal of the inlet when the damper is in the closedposition.
 7. The housing assembly of claim 1 further comprising: a sealcoupled to a perimeter of the damper and adapted to sealingly engage thehousing to providing a bubble-tight seal of the inlet when the damper isin the closed position.
 8. The housing assembly of claim 1, wherein theseal further comprise: at least one of a gasket, fluid seal or abladder.
 9. The housing assembly of claim 1, wherein the linear drivemechanism further comprises: a shaft coupled to the damper engaged witha feature that prevents rotation of the damper when the shaft is movedin a linear direction.
 10. A housing assembly, comprising: a housinghaving an inlet and outlet; a damper disposed in the housing andlinearly movable between positions that open and close the inlet, thedamper having a non-planar shape that extends into the inlet when thedamper is in the closed position; and means for restraining the damperfrom rotating.
 11. The housing assembly of claim 10, wherein the meansfor restraining further comprises: a first feature coupled to thehousing and fixed in orientation relative to the housing; and a secondfeature fixed in orientation relative to the damper, wherein the secondfeature engages the first feature in a manner that permits linear motionwithout rotation.
 12. The housing assembly of claim 10, wherein themeans for restraining further comprises: mating threaded members havingtruncated crests and valleys.
 13. The housing assembly of claim 10,wherein the means for restraining further comprises: a shaft coupled tothe damper, the shaft having a non-circular cross section; and a bearingor guide circumscribing the shaft, the bearing or guide having a shaftaccepting aperture mating the shape of the shaft.
 14. A housingassembly, comprising: a housing having an inlet port, an outlet port anda bag in/bag out filter access port; a filter receiving mechanismdisposed in the housing, the filter receiving mechanism configured todirect gases flowing between the inlet and outlet ports through a filterinstalled in the housing; a first damper disposed in the housing andmovable between positions that open and close the inlet port; a seconddamper disposed in the housing and movable between positions that openand close the outlet port; a mechanism disposed in the housing andconfigured to move the first damper between the open and closedpositions without rotating the first damper, wherein the first damper isspaced apart from the housing when in the open position.
 15. The housingassembly of claim 14, wherein the damper is substantially conical. 16.The housing assembly of claim 14, wherein the mechanism is at least oneof a cam, a scissor actuator, a linear actuator, a power screw, asolenoid, an electric motor, a pneumatic cylinder, a hydraulic cylinderor a gear.
 17. The housing assembly of claim 14 further comprising: aseal interfacing the first damper and the housing to providing abubble-tight seal of the inlet when the first damper is in the closedposition.
 18. The housing assembly of claim 14 further comprising: aseal coupled to a perimeter of the first damper and adapted to sealinglyengage the housing to providing a bubble-tight seal of the inlet whenthe first damper is in the closed position.
 19. The housing assembly ofclaim 18, wherein the seal further comprise: at least one of a gasket,fluid seal or a bladder.
 20. The housing assembly of claim 14, whereinthe mechanism further comprises: a shaft coupled to the damper engagedwith a feature that prevents rotation of the damper when the shaft ismoved in a linear direction.
 21. The housing assembly of claim 14, thefirst damper has a non-planar shape that extends into the inlet when thefirst damper is in the closed position.